Adobe Flas
 

I need to install x-shockwave-flash and Mozilla can't add it to the add-ons/plugins.
Any thoughts?

Which distribution are you using?

Most every package manager includes Flash. Or you can directly download Flash from Adobe. Installation is pretty darn easy, even if you do it manually without the package manager.

Hi and welcome to LQ!
What did you do? Errors?

Assuming you are the only user (or have the only user account) then just find the file libflashplayer.so and move it to ~/.mozilla/plugins/
I don't know what this means but Mozilla isn't that one who adds the plugins. You add the plugins.
jdk

I've found over the years that Firefox can almost never install Flash on its own. It takes user intervention... fortunately, it is pretty easy.

What distribution are you using and what were the errors (if any)?